This paper proposes a hardware configuration for uplink multiuser multiple-input multiple-output (MU-MIMO) transmissions with distributed antenna systems (DASs) in real indoor environments. Beam-forming (BF) technology is used in the DAS with massive MIMO. In massive MIMO transmission, signal processing becomes complicated because of the massive antennas. Therefore, in general, a technique known as digital beamforming (DBF) is adopted, in which the weight values are calculated through digital signal processing. Massive MIMO systems applying DBF, which requires receivers for all massive antennas, have problems related to power consumption and cost because the access point becomes large.
We propose an analog–digital hybrid configuration, which selects antennas using a many-to-one switch connected to the antenna. In the proposed configuration, it is possible to reduce the number of receivers required, by grouping antennas using many-to-one switches. In this paper, we evaluate the effect of the proposed configuration through computer simulations using the propagation channels obtained from experiments conducted in real indoor environments. The effectiveness of the proposed configuration is demonstrated by comparing the basic characteristics, when antennas are selected according to the conventional full-digital configuration and the proposed analog–digital hybrid configuration.
Mobile fronthaul (MFH) is the optical link between a central unit (CU) and a distributed unit (DU) in centralized radio access network (C-RAN) architecture. To suppress the cost of MFH, we have studied MFH networking based on a time division multiplexed passive optical network (TDM-PON). We have proposed low-latency uplink forwarding with a mobile dynamic bandwidth allocation (M-DBA) scheme. When the M-DBA scheme is employed, the uplink latency can be suppressed compared with fixed bandwidth allocation (FBA). In this paper, we clarify the number of ONUs that can be accommodated by the M-DBA scheme when also accommodating a novel functional split based C-RAN.
The reflection and scattering effects of ionosphere can cause clutter interference to the receiving signal of high frequency surface wave radar (HFSWR), which makes it difficult to analyze the spectrum of signal echo. In order to separate the second-order spectrum with wave information component from spectrum containing ionospheric clutter interference, we propose a hybrid echo signal processing algorithm. That is, analyzing the ionospheric signal characteristics for a specific water’s latitude and on the basis of the existing elimination algorithm, according to the characteristics of large scale steady state of the ocean, we introduce parameters such as coherence time and distance value, making an intensive study of the diving method of second-order spectrum area, and obtaining a new extraction algorithm with regional characteristics and strong pertinence. Experimental results show that this method is effective.
In this paper, the authors have proposed an optimization design method for arbitrarily shaped resonant elements with wideband property and have constructed an offset-feed reflectarray by the optimized elements in the X band. Its radiation pattern has been also investigated numerically and experimentally. Usefulness of the proposed method has been proved from comparison between the measured radiation pattern and the calculated ones.